The present invention relates to a speed increaser.
Japanese Patent Application Publication 2004-308757 discloses a speed increaser including an annular peripheral wall that is rotatable with the rotation of a low-speed shaft, a high-speed shaft that is disposed within the ring member and three rollers that are disposed within the ring member and in contact with the peripheral wall and the high-speed shaft. In this speed increaser, when the low-speed shaft is rotated with oil sufficiently supplied, an oil film is formed at positions where the rollers are in contact with the peripheral wall and with the high-speed shaft, and the rotation of the low-speed shaft is transmitted to the high-speed shaft through the oil film thereby to rotate the high-speed shaft at a speed greater than that of the low-speed shaft.
A speed ratio of the speed increaser of the above-cited Publication is determined by the ratio of the inner diameter of the ring to the outer diameter of the high-speed shaft. In order to increase the speed ratio in a speed increaser having a peripheral wall with a constant inner diameter, for example, the diameter of the high-speed shaft may be reduced and the diameters of the rollers may be set so that the power of the low-speed shaft is transmitted to the high speed shaft.
In the above speed increaser having a configuration in which the high-speed shaft is supported by three rollers disposed within the ring member, the high-speed shaft may be supported more stably, as compared with the case in which the high-speed shaft is supported by two rollers. In order to increase a speed ratio in the speed increaser having three rollers, interference between the rollers, which may be caused by an increase of the diameter of the rollers, need be considered, so that the diameter of the high-speed shaft may be reduced only within a range that cause no interference of the rollers. As a result, there is a fear that a desirable speed ratio may not be achieved.
The present invention, which has been made in light of the above problems, is directed to providing a speed increaser that uses three rollers and permits achieving a desired speed ratio.